Geomechanics and Geophysics for Geo-Energy and Geo-Resources最新文献

Dynamic failure widely exists in rock engineering, such as excavation, blasting, and rockburst. However, the quantitative measurement of the dynamic damage process using experimental methods remains a challenge. In this study, a SHPB modeling technique is established based on Voronoi-based DDA to study the damage evolution of Fangshan granite under dynamic loading. The assessment of cracking along the artificial joints among Voronoi sub-blocks is conducted using the modified contact constitutive law. A calibration procedure has been implemented to investigate the rock dynamic properties quantitatively. The dispersion and damping effect can be effectively eliminated by regular discretization in SHPB bars, based on which the dynamic stress equilibrium can be satisfied. To reproduce the loading rate effect of the dynamic compressive strength, which has been observed in the experiment, a modification strategy considering the influence of the rate effect on the strength meso-parameters is proposed. Using this strategy, the peak stresses of the transmitted waves predicted by DDA match well with those obtained from experiments conducted at different loading rates. The simulation results show that more microcracks are generated and the proportion of tensile cracks decreases as the loading rate increases. Furthermore, the dynamic mechanical behavior and fracturing process have also been discussed and compared with the experiments. The results show that the established SHPB system is a powerful tool for quantitative analysis of rock dynamics problems and can handle more complex problems in the future.

To explore the progressive damage and fracture mechanics characteristics of brittle rock materials under combined dynamic-static loading. Taking account of the coupling effect of the constraint states of uniaxial stress (σ₁ ≥ σ₂ = σ₃ = 0), biaxial stress (σ₁ ≥ σ₂ > σ₃ = 0) and true triaxial stress (σ₁ ≥ σ₂ ≥ σ₃ ≠ 0) and impact load, the strain rate effect and prestress constraint effect of dynamic mechanical characteristics of sandstone are studied. The progressive damage evolution law of sandstone under the coupling of true triaxial stress constraint and cyclic impact load is discussed. The results show that with the increase of axial stress σ₁, the dynamic compressive strength and peak strain gradually decrease, and the strain rate gradually increases, resulting in crushing failure under high strain rate. When the axial stress is fixed, the lateral stress constraint reduces the damage degree of sandstone and improves the dynamic compressive strength. With the increase of strain rate, the sample changes from slight splitting failure to inclined shear failure mode. Under the true triaxial stress constraint, the intermediate principal stress σ₂ obviously enhances the dynamic compressive strength of sandstone. Under the constraints of triaxial stress, biaxial stress and uniaxial stress, the enhancement effect of dynamic compressive strength and the deformation resistance of sandstone are weakened in turn. Under the coupling of true triaxial stress constraint and high strain rate, sandstone samples show obvious progressive damage evolution effect under repeated impacts, and eventually inclined shear failure occurs, resulting in complete loss of bearing capacity.

Abstract

The Weibull distribution is used to describe the heterogeneity of rock hydraulics and embedded into the Fish program which is based on the discrete element method. The developed program overcomes the limitation of the Universal Distinct Element Code (UDEC) software regarding the number of parameter groups, which cannot exceed 50. A method for parameter assignment of heterogeneous rocks is proposed together with a method for estimating the initial flow rate value of heterogeneous models. Based on the established heterogeneity calculation model, the influence of block homogeneity, hydraulic aperture homogeneity, and stress on the seepage characteristics is studied. The results indicate that under zero stress conditions, the flow rate is positively correlated with N^0.5 showing a strong linear relationship. The linear relationship is gradually enhanced with the increase in the shape parameters. The relationship between the flow rate and shape parameters is logarithmic with a correlation coefficient greater than 0.9654. The relationship between the flow rate and the axial pressure and confining pressure can be described by quadratic and cubic polynomials, respectively, based on which we further discuss the variation characteristics of equivalent hydraulic apertures under the various axial pressures, confining pressures, and shape parameters.

Motivated by hydraulic stimulation of enhanced geothermal systems, the present paper investigates the coupled thermo-hydro-mechanical response of a geothermal well imbedded in a thermoporoelastic medium, subjected to a non-isothermal fluid flux and convective cooling on the borehole surface. Our focus centers on the effect of local thermal non-equilibrium (LTNE) on the temporal-spatial evolution of temperatures, pore pressure, and stresses, where the solid and fluid phases have two distinct temperatures and local heat transfer between the two phases is addressed. We employ integral transform and load decomposition techniques to derive analytical solutions in the Laplace domain. This methodology allows us to disentangle and separate the individual contributions to changes in pore pressure and stresses from fluid injection and convective heat transfer. The results reveal that compared to the classical local thermal equilibrium model, the thermally induced pore pressure is slightly lower under LTNE conditions. The LTNE has a significant influence on the temporal evolution of thermally induced stresses, especially in the vicinity of the wellbore.

Repurposing a closed mine as lower reservoir is a cost-effective way for the construction of pumped storage hydropower (PSH) plant. This method can eliminate the expenses of mine reclamation, reservoir construction, and land acquisition, resulting in significant cost savings and benefits for the PSH project, known as the PSH benefit. The construction of PSH plants within a closed mine is divided into surface mode and semi-underground mode in this paper. Through a general comparison of two in-situ cases, the finding highlight that the surface mode can achieve a larger potential installed capacity and lower construction cost. Furthermore, the PSH benefit is quantified and internalized as an economic parameter in the ultimate pit limit (UPL) optimization by allocating it into unit ore. Taken an undisclosed open-pit iron mine as example, the UPL is optimized by considering the PSH benefit. The internalized PSH benefit is calculated to be 6.59 CN¥/t when the installed capacity is 2000 MW, and ore amount within the optimized UPL is increased by 1.4%. The results indicated that the PSH benefit does influence the shape and size of UPL, but not significantly. Besides, converting several bottoms in a single open-pit into lower and upper reservoirs presents more challenges for UPL optimization, which further explorations is needed.

In order to explore the influence of natural fractures on the mechanical properties and failure modes of shale at the micro scale, uniaxial compression numerical experiments were conducted on the shale of the Niutang Formation in northern Guizhou with different natural fracture angles using a rock failure process system and digital image processing technology. It is shown that the compressive strength of shale increases with the increase of natural crack inclination, and the growth rate of shale compressive strength also increases. Shale's microscopic fractures can generally be classified into four categories. The first category is to sprout along the natural cracks to the outside of the shale, and eventually form a crack similar to the "X" type (0°); the second category is to sprout along the natural cracks to the middle and outside of the shale, and eventually form an inverted "Y" type crack (15°, 30°); the third category is to sprout along the natural cracks to the middle and outside of the shale, and eventually form an inverted "Y" type crack (15°, 30°); the second type sprouts along the natural fractures toward the middle and outside of the shale, forming inverted "Y"-type fractures (15°, 30°); the third type cracks along the sides of the natural fractures, forming "Y"-type fractures (45°); and the fourth type does not crack along the natural fractures, forming "S"-type fractures (60°, 75°, and 90°). In the low natural fracture dip shale model, tensile damage mainly occurs, accompanied by a small amount of compressive shear damage; in the high natural fracture dip shale model, tensile damage and compressive shear damage account for a larger proportion in the fracture process.This suggests that the presence of natural cracks in shale has a significant impact on stress distribution. There are two main types of acoustic emission signal distribution and evolutionary features, the evolutionary features of acoustic emission signal distribution are of two types, 0°-45° test and 60°-90° test, and the difference is mainly reflected in the damage stage, the damage of shale with high natural fracture inclination is more intense, which is manifested by the decrease in the number of acoustic emission events, but the level of acoustic emission events in the damage stage is higher, which can reach 61788, 46605 and 94315, the shale with high natural fracture inclination is more brittle.

During the operation of artificial underground structures, the surrounding rock experiences fatigue and creep damage caused by several types of disturbances under long-term constant loading. To quantify the mechanical response of sandstone under creep–fatigue loading, a damage–hardening evolution model based on the linear superposition concept is proposed. In the model, coupling is applied to represent the synergistic effect of creep and fatigue. Creep–fatigue tests of sandstone specimens are conducted under multilevel loading. The damage and hardening effects of sandstone under creep–fatigue loading are complex. Hardening is the dominant effect under low creep–fatigue loads, and damage is the dominant effect under high creep–fatigue loads. The strength of the rock specimens undergoes increasing and decreasing trends under this loading path, and the evolution of the Mohr–Coulomb envelope is discussed. The proposed model can be used to describe the test data and the evolution of the creep–fatigue process. With increasing creep–fatigue number, the acoustic emission amplitude, energy, and cumulative counts increase. However, the amplitude is more sensitive than the energy, indicating that it is more suitable for describing creep–fatigue loading. Furthermore, the peak frequencies of the AE signals are mostly distributed in the 0–15 kHz, 15–30 kHz, 30–45 kHz, and 45–55 kHz regions. The signal proportion in the 45–55 kHz zone decreases with the creep–fatigue number. However, other frequency zones increase with the creep–fatigue number. This phenomenon illustrates that the crack scale of the specimens increases with the creep–fatigue number.

Water damage in mines poses a widespread challenge in the coal mining industry. Gaining a comprehensive understanding of the multi-factor spatial catastrophe evolution mechanism and process of floor water inrush is crucial, which will enable the achievement of dynamic, quantitative, and precise early warning systems. It holds significant theoretical guidance for implementing effective water prevention and control measures in coal mines. This study focuses on the issue of water inrush in the coal seam floor, specifically in the context of Pengzhuang coal mine. By utilizing a small sample of non-linear characteristics derived from drilling geological data, we adopt a multifactor spatial perspective that considers geological structure and hydrogeological conditions. In light of this, we propose a quantitative risk prediction model that integrates the coupled theoretical analysis, statistical analysis, and machine learning simulation methods. Firstly, the utilization of a quantification approach employing a triangular fuzzy number allows for the representation of a comparative matrix based on empirical values. Simultaneously, the networked risk transmission effect of underlying control risk factors is taken into consideration. The application of principal component analysis optimizes the entropy weight method, effectively reducing the interference caused by multifactor correlation. By employing game theory, the subjective and objective weight proportions of the control factors are reasonably allocated, thereby establishing a vulnerability index model based on a comprehensive weighting of subjective and objective factors. Secondly, the WOA-RF-GIS approach is employed to comprehensively explore the interconnectedness of water diversion channel data. Collaborative Kriging interpolation is utilized to enhance the dimensionality of the data and facilitate spatial information processing. Lastly, the representation of risk is coupled with necessary and sufficient condition layers, enabling the qualitative visualization of quantitative results. This approach aims to accurately predict disaster risk with limited sample data, ultimately achieving the goal of precise risk assessment. The research findings demonstrate that the reconstructed optimization model based on multi-factor spatial game theory exhibits high precision and generalization capability. This model effectively unveils the non-linear dynamic processes associated with floor water inrush, which are influenced by multiple factors, characterized by limited data volume, and governed by complex formation mechanisms. The identification of high-risk areas for water inrush is achieved with remarkable accuracy, providing invaluable technical support for the formulation of targeted water prevention and control measures, ultimately ensuring the safety of coal mining operations.

Evaluation of seismic attributes and seismic reflection characteristics analysis of Razzak Field was undertaken by subdividing the study area rock units. There are four seismo-facies units of varying parameters from top to bottom. These units are comparable to the Apollonia and Khoman Formations; the Abu-Roash Formation; Baharyia Formation and Alamein Formation. The seismo-facies unit 1 of the Apollonia and Khoman Formations reveal parallel to sub-parallel layering, with thickness increases northwards. The lithological distribution consists of limestone with minor clay intercalations with facies varying from middle neritic graded to outer neritic. Unit 2 of the Abu-Roash Formation shows divergent layering, with a thickness increasing gradually northwards and eastwards. The lithological distribution shows predominance of carbonate, sandstone occurring in minor portions and laterally graded into shale with littoral facies ranging to inner and middle neritic facies. Unit 3 of the Baharyia Formation reveals chaotic and oblique layering with a time thickness increases towards northeast and southwest parts, the lithological distribution exhibited sand and shale with minor limestone streaks, with facies varied changed from continental to inner-middle neritic, unit 4 of the Alamein Formation shows variation from parallel-subparallel orientation to oblique and chaotic with thickness increasing towards northwards and eastwards, the lithological distribution exhibited dolomitic limestone with minor streaks of limestone with facies varied from middle neritic facies to outer neritic and bathyal. Finally, the results are integrated to build up a seismo-stratigraphic model of the evaluated area of the northwestern Desert of Egypt. Seismic interpretation involves the construction of structure contour maps, in terms of time and depth, on the tops of the Apollonia, Abu-Roash, Baharyia and Alamein Formations. These maps show three structural closures, due to folding, that are dissected by NW–SE faults, analysis of relevant structural and stratigraphic seismic attributes such as root-mean-square amplitude, local structural dip, variance, ISO frequency component, sweetness and acoustic impedance average energy applied on reservoir tops, to enhance the visibility of faults, geological interpretation and the physical parameters of the subsurface related to lithology and stratigraphy for reservoir characterization. Finally, the results obtained are used to construct a seismic structural model. Integration of seismic and stratigraphic data is used to build a geological model of the northwestern Desert of Egypt.

Caving activity results in an increased induced seismicity which should be monitored to avoid massive and uncontrolled rock damage. This research was conducted at the Deep Mill Level Zone (DMLZ) underground mine, the deepest underground mine in Indonesia operated by PT Freeport Indonesia. This research aims to monitor cave propagation by using 4D tomography with a catalogue of microseismic for 57 days with a total of 14,821 events recorded by 84 stations consisting of 176,265 P phases and 133,472 S phases. The data is divided into four subsets to see the velocity evolution related to cave progress. Checkerboard Resolution Test (CRT) and Derivative Weight Sum (DWS) are used to assess the resolution of the inversion. 3D initial velocity model is constructed based on geological information and coring data. We have succeeded in identifying the interpreted cave propagation of a 60 m extension to the NW at around 100 m above undercut level based on 4D changes in velocity tomogram validate by Time Domain Reflectometry data. The decrease of Vp and Vs in subset 3 is interpreted due to the fracturing processes as the cave progresses. Furthermore, we observe a stress redistribution along with the progress of the cave, which is characterized by high velocities (Vp and Vs) due to compensation for changes in low velocity values ​​in the area in front of the cave, which is starting to collapse. We suggest that a considerable change in the velocity tomogram as an indicator of impending caving.